Whether Head Start is able to reduce the achievement gap and indeed whether it "works" has been a hotly debated topic since its inception, and legislative pressures to demonstrate program performance and accountability are increasing. Evaluation of its effectiveness has had a somewhat checkered past, partly because of changes in program philosophy, debates about the most appropriate and expectable outcomes from the program, and the evaluation methods that can best demonstrate these effects. In particular, several key questions have emerged, broadly stated as follows: 1. What is the quality of Head Start classrooms as early learning environments, how does it compare to other early childhood education settings, and what factors predict variations in quality? 2. Do children make significant gains in their school-readiness skills during the Head Start year and into kindergarten, and are these gains due to their exposure to Head Start? 3. Is program quality related to children's gains during Head Start and into kindergarten? 4. What difference does participation in Head Start make to key school-readiness outcomes and parental practices for children and parents from low-income families? 5. Under what circumstances does Head Start achieve the greatest impact? What works for which children? Which Head Start services are most related to impact? To answer these key questions, this chapter reviews the state of the national Head Start program, with emphasis on the findings from the Head Start Child and Family Experiences Survey (FACES) and the Head Start Impact Study (HSIS). (author abstract)